Optical fiber connectors commonly use ferrules to insure alignment of the fibers. Typically two fibers that are to be connected are inserted into housings having matching ferrules attached thereto. The ends of the fibers are then polished to produce a smooth optical finish and the ferrules are inserted into a central housing that holds them close together and in precise alignment.
The term "connector" is often used in a variety of ways in the field of fiber optics. Sometimes it is used to refer to two of the housings with ferrules as described above along with the central housing. At other times it is used to refer to a single housing with a ferrule. This later definition will be adopted herein. Thus, in order to connect two optical fibers, two connectors and a central housing are required.
The ferrules used in fiber optic connectors come in many shapes and can be of many of different materials. Typically the ferrules are of a ceramic material, although metallic or plastic materials can also be used. The ferrule may be cylindrical, as in the widely used ST connector defined by proposed EIA Specification 475E000 or in an SC connector, or it may be a truncated cone as in the case of a biconic connector.
In order to insure a good optical connection, as well as the structural integrity of the connector, the fiber must be tightly bound in the connector. Typically this is done by use of an adhesive. Most commonly an epoxy is used to hold a fiber in a connector housing and ferrule. Once an epoxy has hardened, it cannot be loosened. Thus, if a fiber is incorrectly installed in a connector housing and ferrule, or is damaged subsequent to such installation, the housing and ferrule cannot be reused. U.S. Pat. No. 4,984,865 (Lee et al.) describes the use of a hot melt adhesive to hold a fiber in a fiber optic connector. While this has the advantage of being reusable, it requires that the assembly be heated above the softening temperature of the adhesive upon either insertion or removal of a fiber.
A disadvantage of both epoxies and hot melt adhesives is that both require a delay from the time the fiber is installed in order to harden the adhesive. In addition a hot melt adhesive always requires the use of a heating fixture. The heating fixture, in turn, must be powered, sometimes causing inconvenience. An epoxy does not necessarily require the use of a heating fixture, but, for the epoxies typically used in fiber optic connectors, the cure period will be several hours if no heat is applied. Thus epoxies offer a tradeoff between the inconvenience of a long cure period and that of the use of a heating fixture. Alternatively some epoxies require a source of ultraviolet radiation for curing. Such a radiation source still has the requirement that it be powered.
U.S. Pat. No. 4,964,685 (Savitsky et al.) teaches a fiber optic connector in which the fiber is mechanically clamped in the ferrule by a gripping element. In a connector according to the Savitsky et al. patent, however, the gripping element grips the fiber's buffer instead of the fiber itself. Since it is possible for the fiber to move inside of the buffer, it is difficult to precisely align the end of the fiber with the end face of ferrule. This difficulty is increased by the fact that the gripping element is collapsed onto the fiber buffer by moving a nut along the connector in a direction parallel to the fiber. Thus the force and movement required to engage the gripping element are directed parallel to the fiber. This can cause the fiber to move in the ferrule as the gripping element is tightened.